The present invention relates to paving screed assemblies, and more particularly to paving screeds with screed extensions.
Screed assemblies 1 used with paving machines to level paving material, typically asphalt, applied by the machine onto a generally horizontal base surface 2 are well known, an example of such being depicted in FIGS. 1 and 2. Such screed assemblies 1 often include both a main screed 3 and one or more pairs of screed extensions 4 connected with the main screed 3. The screed extension 4 may either be fixedly attached (e.g., bolted) to an end of the main screed 3 (or an outer end of another screed extension 4) or movably attached to the main screed 3. Movably attached screed extensions 4 are commonly referred to as "extendible screeds" and are laterally displaceable with respect to the main screed 3, typically by means of hydraulic cylinders (not shown) so as to either be extended outwardly beyond the outer ends 3b of the main screed 3 or retracted into centralized positions. Both types of screed extensions 4 enable the screed assembly 1 to be adjusted for use in paving different base surfaces 2 of various widths.
Typically, the extendible screeds 4 are attached to the main screed 3 such that the screed extension 4 is disposed either frontwardly or rearwardly of the main screed 3, and move along the front or rear vertical surface, respectively, of the main screed 3. As shown in FIG. 2 for a "front-mounted" screed extension 4, each screed extension 4 is typically connected to the main screed 3 so as to be vertically suspended from a pair of laterally spaced support members 6. With this construction, the screed extensions 4 are only prevented from swinging or pivoting about the support members 6 due to the fact that a "floating" screed assembly 1 is generally tilted rearwardly, such that the rear vertical surface 4b of the screed extension rests against (and is thus supported by) the front surface 3b of the main screed 3. As the screed assembly 1 moves forwardly during a paving operation, contact with the paving material also tends to "push" the screed extensions 4 rearwardly into contact with the main screed 3. As the screed extensions 4 are connected to and supported by the main screed 3, the screed extensions 4 essentially follow or "mimic" the movement of the main screed 3. Thus, when the main screed 3 is rotated about a longitudinal or laterally-extending axis 1b of the screed assembly 1 (FIG. 1) in order to adjust the assembly 1 angle of attack .alpha. (as described below), the screed extension 4 rotates with the main screed 3.
In order to control the depth of the finished "mat" of paving material, the "angle of attack" .alpha. of the screed assembly 1 (FIG. 2) may have to be adjusted. The main screed 3 is "tilted" forwardly or rearwardly about axis 1b to position the main screed working surface 3a at the desired angle of attack .alpha.. Due to the rotation of the main screed 3 to the desired angle .alpha., the screed extensions 4 also rotate so as to be positioned at substantially the same angle of attack .alpha.. In certain paving projects, it has been determined that having a lesser angle of attack .alpha. at the outer edges of the screed assembly 1, i.e., the areas leveled by the screed extensions 4, favorably modifies the "flow" of paving material such that a better finished mat of material is produced. However, with known screed assemblies 1 as described above, the screed extensions 4 are merely adjustable vertically with respect to the main screed 3 in order to position the extension working surface 4a at substantially the same height as the main screed working surface 3a. With such screed assemblies 1, the screed extensions 4 are substantially prevented from being angled or tilted with respect to the main screed 3 due to the above-described abutting relation between the rear surface 4b and the front surface 3b of the screed extension 4 and the main screed 3, respectively.
Therefore, it is desirable to provide a screed assembly with screed extensions 4 having the capability of adjusting the angle of attack .alpha. of the screed extension working surface 4a relative to the working surface 3a of the main screed 3. Further, it is desirable to provide such an adjustment capability as a retro-fit to exiting screed assemblies.